In a semiconductor manufacturing process, lithography is employed as a technique of drawing patterns on a wafer. In lithography, various patterns formed on a mask are demagnified and transferred to a wafer using light beams. The mask patterns used in the lithography require extraordinary precision. A charged-particle-beam exposure apparatus is employed to form such mask patterns. A charged-particle-beam exposure apparatus is also used for directly drawing patterns on a wafer without using a mask.
Charged-particle-beam exposure apparatuses include a point-beam type, which irradiates a spot-like beam, and a variable-rectangular-beam type, which irradiates a beam having a variable rectangular cross section. Regardless of the configuration, the charged-particle-beam exposure apparatus generally comprises an electron gun unit for generating a charged-particle beam, an electron optical system for introducing the beam generated by the electron gun to a sample, a stage system for scanning the entire surface of the sample relative to the electron beam, and an objective deflector for positioning the electron beam on the sample surface with high precision.
A charged-particle beam has an extraordinarily high response. Therefore, rather than improving the mechanical and regulatory characteristics of the stage, it is a general procedure to adopt a system that measures an error in the posture and position of the stage and feedbacks the error to positioning of the beam by a deflector which causes a charged-particle beam to scan.
The stage is provided in a vacuum chamber and constrained not to cause magnetic field fluctuation that influences the positioning of a charged-particle beam. For this reason, conventionally, all that is required is for the stage to move in a two-dimensional direction. The stage is configured with limited contact-type components, e.g., a rolling guide, a ball screw actuator, or the like. Therefore, the conventional contact-type components raise problems of lubrication and dust generation. To cope with these problems, the conventional art has proposed a construction shown in FIG. 1, which employs electromagnets (1, 2) as a driving element of the XY stage. Japanese Patent Application Laid-Open No. 11-194824 discloses a non-contact six-degree-of-freedom stage mechanism which employs electromagnet actuators and magnetic shields. The method disclosed in this document allows less fluctuation of leakage flux and assures a highly immaculate environment. Therefore, it is applicable to a positioning apparatus in a vacuum environment and enables highly precise positioning operation.
Higher precision in exposure operation and higher speed in stage driving are further demanded to improve a throughput of the exposure apparatus. However, to meet such demands, the non-contact six-degree-of-freedom stage mechanism employing electromagnet actuators and magnetic shields, which is disclosed in the aforementioned document, raises a problem of a complicated structure of the magnetic shield portion. In other words, due to the massive structure of the magnetic shield portion, the weight of the movable portion of the stage increases. Therefore, it has conventionally been difficult to achieve high acceleration/deceleration of the stage and high-speed positioning at the cost of the servo rigidity of the driving system which includes the above-described components.